A surface of a substrate formed from glass, metal, plastic, ceramics, or the like has been modified depending on a purpose in various fields in the related art. For example, a fluorine-containing silane-based coupling agent is coated on a surface of glass or plastic so as to apply water repellency or oil repellency to the surface.
An organic metal compound such as a fluorine-containing silane-based coupling agent carries out a hydrolysis-polycondensation reaction to form a film. In the invention, this film is referred to as an organic metal thin film.
As a method for forming the organic metal thin film to modify a substrate surface, for example, the following methods are known.
(1) PTL 1 to PTL 3 disclose a method for producing a chemical absorption film in which peeling resistance and transparency are high and which does not deteriorate glossiness of a substrate surface or transparency of the substrate.
(2) PTL 4 discloses a method for forming a chemical absorption film. In the method, a mixed solution, which contains at least an alkoxy silane-based surfactant, a non-aqueous solvent not containing active hydrogen, and a silanol condensation catalyst, is brought into contact with the substrate surface, and the chemical absorption film is covalently bonded through a siloxane bond.
(3) NPL 1 discloses a method for forming a crystalline monomolecular film by developing an organic solvent solution of a silane-based surfactant on a silicon wafer surface onto which purified water is supplied dropwise.
(4) PTL 5 and PTL 6 disclose a method for fixing a water-repellent film constituted by a monomolecular layer to a substrate surface through a silanol group using a monomer or a polymer of a hydrolysate of a fluoroalkyl group-containing silane compound that is hydrolyzed under an acid catalyst.
(5) PTL 7 discloses a method for producing a condensation product by hydrolyzing and condensing an organic metal compound using an acid catalyst and a specific polar solvent. The condensation product has an OH group, and the hydrolysable group derived from the organic metal compound is appropriately present without being completely decomposed, and thus the condensation product contains a condensation product with a low degree of condensation.
In addition, NPL 2 discloses a technology of obtaining white powder by hydrolyzing and condensing triethoxy alkyl silane. However, NPL 2 does not disclose that the white powder is dissolved in an organic solvent and the resultant solution is used as an organic thin film-forming solution.